Traffic camera law enforcement has traditionally used 35 mm film-based cameras for the detection of speed and red-light violations.
In the case of red light violations, the camera is used in conjunction with vehicle detection systems that are usually in-ground (in-road) sensors eg inductive loops, which detect the presence of a vehicle at a particular point on the roadway. The camera system is also connected to the traffic signal controller, generally the red feed for the purpose of co-coordinating to the red signal phase. In principle an image of an offending vehicle is taken when a vehicle is detected about to enter the intersection, and/or in the intersection during the red signal phase. A common practice is to take two (2) images of a vehicle as it progresses through the intersection in order to provide sufficient evidence for a prosecution.
With speed violations, similar film-based cameras are used with a speed-measuring device—either in-ground loops for fixed-speed traps, or radar commonly used by mobile speed enforcement units. For speed enforcement, a picture of the vehicle is captured when the speed measuring system detects a vehicle traveling at a speed in excess of a preset threshold speed.
The film-camera systems have required white light illumination generally in the form of flash units, to provide sufficient light to capture violation images in poor ambient light or at night.
With the advent of digital imaging traffic cameras the film-based cameras are being replaced by digital cameras however the violation detection and recording and illumination systems have remained fundamentally as for film-based operations.
Similarly while the advent of digital cameras is removing the need to digitise film images to allow automated processing and allows the option of centralised processing, processing software still has to be installed and maintained locally in each processing or user location. Additionally, users other than authorized processing officers must typically request issue of violation information according to standard formats or reports and are barred from interactivity with system data.
The fundamental disadvantages of these commonly applied systems are:    (a) The detection system is invariably unable to provide a trigger point that is sufficiently consistent to ensure that the positioning of vehicles at the time of imaging is identical. To compensate for this a wider angle lens is used with the consequence of reducing the available resolution for effective and efficient license plate recognition during subsequent evidence processing;    (b) Conventional system's typically capture a single image of the vehicle licence plate. If this image is obscured or poorly focussed, it may be impossible to identify the vehicle. Likewise, with only one image of the driver, it may be difficult or impossible to provide an identifiable driver image where this is required;    (c) High construction and maintenance costs (ie because of the costs of installing and maintaining in-ground sensors, underground cabling and connections to traffic signal controllers, flash units and in some instances where digital cameras are used, communications lines);    (d) The use of flash illumination may be detrimental at night to oncoming traffic and has the potential to cause temporary driver blindness and consequent safety risks as well as preventing authorities from deploying systems covertly;    (e) The requirement to install flash illumination units (often on a separate pole) also incurs additional supply, installation, maintenance and running costs and creates additional visual pollution;    (f) Where digital cameras are used, systems either require the availability of high-speed communications lines to meet the demands of communicating high-resolution images, or else images and data must be collected manually;    (g) Purpose built, high-resolution, digital traffic cameras are relatively expensive, adding to costs of traffic program installations and operation.    (h) Traffic violation evidence collected by conventional systems includes time and data information provided by the camera computer clock which can be subject to error and therefore can prejudice the validity of evidence.    (i) The requirement that violation processing software be installed and maintained in all computers in all processing offices and on all client computer systems in the various client locations incurs high program implementation and support costs.    (j) With the exception of authorised processing personnel, users of violation evidence such as courts or police departments have been denied interactive access to information held by the central processing system and have only been able to request and view standard reports prepared for them by the relevant processing office.